1. Field of the Invention
The present invention relates to a display control apparatus of a scanning type display. More specifically, the present invention relates to an improvement in a display control for displaying an image symbol on a scanning type display using a character pattern storing memory.
2. Description of the Prior Art
Of late, a so-called video game apparatus for displaying images of a variety of configurations using a scanning type display of such as a cathode-ray tube has been put into practical use. A graphic system and a character system have been well-known as a system for controlling display of images on a cathode-ray display, for example, in a conventional video game apparatus. A typical graphic system is disclosed in U.S. Pat. No. 4,016,362 issued Apr. 5, 1977 to Stephen D. Bristow and Steven T. Mayer. The principle of such graphic system will be briefly described subsequently with reference to FIG. 1. On the other hand, a typical character system is disclosed in U.S. patent application Ser. No. 706,121 now U.S. Pat. No. 4,116,444 filed by July 16, 1976 by Steven T. Mayer. The principle of such character system is also briefly described subsequently with reference to FIG. 2.
FIG. 1 is a block diagram showing one example of a conventional apparatus for controlling display of images on a cathode-ray tube display in accordance with a graphic system. The graphic system display shown is adapted such that a desired character is displayed by a television receiver which is an example of a cathode-ray tube display directly storing information of a variety of characters being displayed on a screen of the television receiver 1 in a random access memory 14 and is referred to as a direct random access memory system.
Now referring to FIG. 1, a structure of a graphic system display shown will be described. Assuming that the screen of the display of the television receiver 1 is constituted by an arrangement of dots, with 256 dots both in the horizontal and vertical directions, the random access memory 14 is adapted to store information of each bit of the screen of the display of the television receiver 1 in one bit position of the memory and to that end the random access memory 14 has a storage capacity of 256.times.256 bits positions. Taking into consideration the fact that a computer or a microcomputer usually used in such video game apparatus comprises a data structure of eight bits, preferably the random access memory 14 is structured to have a capacity of 8129 words, each word being eight bits, i.e. eight kilobytes in total. However, the foregoing discussion is based on the fact that display is made in terms of two values of black and white. As to be described subsequently, the random access memory 14 is controlled to store image data being displayed on the screen of the display of the television receiver 1 and the random access memory 14 is then controlled to provide the stored image data through a read operation.
The central processing unit 11 is responsive to a program stored in advance to generate data being written in the random access memory and address data for specifying the addresses where the data being written is to be written, thereby to perform a write control and also to perform an arithmetic operation in the case where a game is to be played using images being displayed on the screen on the display of the television receiver 1. The write address data being obtained from the central processing unit 11 is applied to an address data switch circuit 12. The data being written or simply write data obtained from the central processing unit 11 is applied to a write/read data switch circuit 15. The switch circuit 12 is connected to receive a synchronizing signal from a synchronizing counter 13 as read address data. The synchronizing signal generated by the synchronizing counter 13 is a signal in synchronism with horizontal scanning and vertical scanning of the television receiver 1. The switch circuits 12 and 15 are also supplied with a switch signal. The switch signal is a write signal of the high level during the vertical blanking period, thereby to select a write mode by switching the switch circuits 12 and 15 to the central processing unit 11. The switch signal also becomes a read enable signal of the low level during the period other than the vertical blanking period, thereby to select a read mode by switching the switch circuit 12 to the synchronizing counter 13 and by switching the switch circuit 15 to a parallel/serial converter 16.
In operation, during the vertical blanking period the switch circuits 12 and 15 are switched to the central processing unit 11, whereby the write mode is established. In the write mode the write address data obtained from the central processing unit 11 is applied through the switch circuit 12 to the random access memory 14. At the same time the write data obtained from the central processing unit 11 is applied through the switch circuit 15 to the random access memory 14. Therefore, the random access memory 14 is loaded with the write data in the addresses designated in high speed.
On the other hand, during a period other than the vertical blanking period the switch circuits 12 and 15 are turned to the read mode. Therefore, the synchronizing signal of the output from the synchronizing counter 13 is applied through the switch circuit 12 to the random access memory 14 as the read address data. As a result, the random access memory 14 is controlled so that the write data is read out. The data as read out from the random access memory 14 is applied through the switch circuit 15 to a parallel/serial converter 16. The parallel/serial converter 16 serves to convert the parallel data of eight bits read out from the random access memory 14 into a serial data format and the converted output is applied through an OR gate 17 to the television receiver 1. At the same time a composite synchronizing signal including a horizontal synchronizing signal and a vertical synchronizing signal is applied through the OR gate 17 to the television receiver 1. As a result, an image symbol or image symbols are displayed on the screen of the display of the television receiver 1 based on the data stored in the random access memory 14. Thereafter the above described operation is repeated per each cycle of the vertical blanking signal.
However, since the graphic system display requires that the random access memory 14 has a capacity of the number of bits corresponding to the number of dots of one screen, the same involves a disadvantage that an increased capacity of high expense is required in performing a colored display and a brightness controlled display. In addition, the central processing unit 11 needs to control a write operation of the data into all the addresses of the random access memory 14 by using a major portion of the processing capability of the central processing unit 11 and therefore the central processing unit 11 cannot be used in brain-like processing such as strategy inherently required in a game by such video game apparatus, which imposed a major restriction in a game. In order to eliminate such restriction in a game, the central processing unit need be of a high speed processing or need be of one which has been specially designed for such brain-like processing such as a strategy in a game. Nevertheless, another disadvantage is involved that such approach makes the cost very expensive.
Accordingly, in order to reduce a storage capacity of a random access memory and to mitigate a burden of a processing capability of a central processing unit, a display of a character system has also been proposed.
FIG. 2 is a block diagram of an example of an apparatus for controlling display of images on a conventional cathode-ray tube display in accordance with a character system. In a character system display shown, the screen of the television receiver 1 comprises an arrangement of a plurality of blocks arranged in 32 rows and 32 columns. Each of the columns is identified by a corresponding ordinal column number being allotted starting from the left end of the screen. On the other hand, each of the rows is identified by a corresponding ordinal row number starting from the top end of the screen. In other words, each of the blocks is allotted the corresponding ordinal column number and the corresponding ordinal row number to indicate the location thereof with the left upper corner of the screen as the origin. Each of the blocks comprises an arrangement of dots arranged in rows and columns, say 8.times.8 dots. In displaying a character at a desired position on the screen, the position is determined by address information representing the column number and the address information representing the row number.
In order to store in advance a plurality of kinds of characters each being displayed as a moving image symbol or object by means of a given block of the lattice, a character storing memory 28 is provided. The random access memory 24 comprises addresses of the number, say 32.times.32=1024 addresses, corresponding to the number of blocks in the lattice on the screen of the television receiver 1. The respective addresses of the random access memory 24 are determined to store information for identifying characters each being displayed as a moving image symbol by a corresponding block. Meanwhile, referring to FIG. 2, the same portions as those in FIG. 1 have been denoted by the same reference characters and a detailed description thereof will be omitted.
In operation, during the vertical blanking period the switch circuits 12 and 15 are switched to the central processing unit 11, whereby the write mode is established. At that time the central processing unit 11 provides through the switch circuit 12 to the random access memory the write address data for designating the respective blocks out of a plurality of blocks being displayed on one screen and also provides through the switch circuit 15 to the random access memory 24 the character identifying information representing the kind of the characters being displayed by the respective blocks. To that end, the random access memory 24 is in succession loaded with the character identifying information at the addresses corresponding to the respective blocks.
On the other hand, during the period other than the vertical blanking period the switch circuits 12 and 15 are switched to the read mode. At that time the synchronizing counter 23 provides the read address data for designating the position in the column number and row number responsive to the horizontal synchronizing signal and the vertical synchronizing signal for controlling the display of the television receiver 1. The read address data is applied through the switch circuit 12 to the random access memory 24. Accordingly, the character identifying information being displayed is read out from the random access memory 24 and is applied through the switch circuit 15 to the character storing memory 28. On the other hand, the synchronizing counter 23 provides to the character storing memory 28 the information designating the row number of the characters being designated by the character identifying information based on the vertical synchronizing signal. Accordingly the character information being displayed on the position of the block in synchronism with the horizontal synchronizing signal and the vertical synchronizing signal is read out in a bit parallel fashion from the character storing memory 28. The character identifying information is converted by the parallel/serial converter 16 into a serial data format and the same is applied through the OR gate 17 to the television receiver 1.
Thus, according to the character system display, the central processing unit merely controls a write operation of the character identifying information into 1024 addresses at the maximum of the random access memory 24 and as a result a processing time period required for controlling image display is drastically shortened. In addition, the character system display can mitigate the burden of the central processing unit 11 and also can decrease a storage capacity of the random access memory 24.
However, while the character system display can be advantageously utilized in a case where still images such as letters, numerals and the like are displayed, the same is not suited for display of a movable image symbol such as displayed in a video game apparatus. The reason will be described in detail with reference to FIG. 3. The character system display can display a desired moving image symbol only at a predetermined position of the coordinates of the blocks of the divided rows and the columns on the screen of the television receiver 1. For example, as shown in FIG. 3, in the case where a given moving image symbol is to be displayed by designating the forth columns (H=4) and the third row (V=3), the designated address of the display position of the moving image symbol is H=4, V=3. In the case where the symbol is to be moved in the rightward direction, assuming that the target address is H=5 and V=3, the symbol is displayed at the position spaced apart in the rightward direction by one column. Similarly, in the case where the symbol is to be moved in the rightward and downward inclined direction, assuming that the target address is H=5 and V=4, the symbol is displayed to be spaced apart in the rightward and downward oblique direction by one block. Therefore, the moving image symbol looks as rapidly flying or moving one block by one block and such movement is observed as unnatural movement.
Meanwhile, in such video game apparatus, it is necessary that character symbols be moved. However, a character system display for moving a symbol on a block by block basis causes an impression that the movement of a moving image symbol is extremely unnatural. Nevertheless, it was hardly possible to show smooth movement of an image symbol. In addition, a character system display involves a limitation to display positions where images can be displayed on the screen of the television receiver 1, i.e. involves a disadvantage that moving symbol images cannot be displayed at any desired number of display positions.